The present invention relates generally to systems for circulating fluids in a body of liquid. More particularly, it relates to a pump for circulating gases or liquids within a body of liquid.
There are many instances in industrial, commercial and domestic operations in which fluids are circulated or mixed within a body of liquid. An example of a domestic use is circulation of water in a home aquarium, in which the water in the aquarium is circulated through a filter to remove suspended solids. In industrial and commercial operations it is frequently necessary to circulate the contents of a tank to keep particles in suspension, or to achieve a uniform admixture throughout the body of liquid. Circulation may be accomplished using pumps, propellers, or other means.
In addition to simply circulating the liquid contents in a body of liquid, it is sometimes desirable to inject other fluids into the liquid. For example, sewage and other waste water is aerated so that noxious organic matter in the waste is oxidized into benign forms. Other examples of aeration include aeration of fermentation broths to provide oxygen for the growth of microorganisms. Similarly, ponds, tanks, and lakes are aerated to sustain the life of aquatic plants and animals, such as in aquariums and live wells.
Essentially, aeration is effected by bubbling air into the aqueous medium. Ideally, the air should be introduced in the form of minute bubbles to maximize the surface area of the interface between gas and liquid and thereby increase the rate of mass transfer. Moreover, the bubbles should be uniformly distributed throughout the body of liquid, and should persist for as long as possible to maximize the amount of oxygen which is transferred to the liquid.
It is, of course, desirable to limit the cost of the equipment used to effect circulation and aeration. Moreover, it is desirable to minimize the amount of energy required to accomplish aeration. The simplest form of aeration apparatus comprises an air compressor together with the necessary piping, tubing, and nozzles or spargers to bubble compressed air into the liquid. Compressors are relatively costly. They are also noisy and inefficient. Moreover, the amount of agitation provided in the liquid by the emerging air is often insufficient to provide good mixing, and auxiliary mixing equipment therefore may be required.
Many types of aeration apparatus have been designed to increase the efficiency of mixing and mass transfer. An example of one apparatus particularly adapted for use in sewage treatment is disclosed in U.S. Pat. No. 2,966,345 to Burgoon et al. In accordance with the ""345 patent, a tubular drive shaft extends vertically into waste water contained in a treatment tank, the shaft rotatably driven by an electric motor. Hollow arms extend outwardly from a hub at the bottom of the shaft, the arms having openings at their outer ends. As the shaft and arms rotate, a sub-atmospheric pressure region is created adjacent the ends of the arms, and air is transported by atmospheric pressure out of the openings and into the liquid. The arms function to mix and agitate the tank contents, and also to discharge a stream of air bubbles into the liquid.
With respect to apparatus to merely agitate the contents of a tank or circulate the same, a variety of approaches have been taken. Propellers and submersible centrifugal pumps fulfill this function, and are widely used. Such apparatus, particularly centrifugal pumps, require substantial machining in their manufacture, with accompanying increased cost.
In accordance with the present invention, a system is provided for circulating fluids, both gases and liquids, in a body of liquid. The system comprises a rotatable shaft having a tubular segment immersed in the body of liquid. The tubular segment of the shaft is in fluid communication with the fluid to be circulated. Means are provided for rotating the shaft. One or more tubular arms extend radially outwardly from the tubular shaft segment, and are in fluid communication with the tubular shaft segment. Each tubular arm comprises an extension spring which, under static conditions, is substantially straight but which upon rotation of the shaft is believed to be arcuately deflected by hydrodynamic force so as to impel fluid into the body of liquid. The system may be utilized for simply circulating the liquid, or for injecting a gas into the body of liquid. The method and apparatus of the present invention are particularly useful in effecting aeration of water to maximize the concentration of dissolved oxygen therein.